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Morrisville, N.C. — Debris in the highway might have been the cause of a four-car collision that killed a 19-year-old on Interstate 40 Friday and caused traffic gridlock that lasted for hours and spanned miles.

Investigators said Joshua Cobb, of Snow Camp, died when the pickup truck he was driving for Graham-based TMI Services careened off I-40 near Aviation Parkway in Wake County and landed in an embankment.

State troopers still don't know Cobb's exact role in the wreck, but they said that the debris had forced traffic to slow down to about 45 mph and that the speed led to the chain-reaction collision.

Authorities said three other people were taken to Rex Hospital with injuries that did not appear to be life-threatening: Zachary Jones, of Raleigh, who was driving a blue Chevrolet truck; and Ansley Meyer and her passenger, Charles Oskins, also of Raleigh, were in a Mitsubishi Montero that flipped.

Sarah Uhland, of Cary, who was driving a Honda, wasn't injured.

"It's kind of undetermined right now who's at fault and what happened," state Trooper Nathan White said. "We've got to get some more information."

A reconstruction team was expected to return to the wreck site Saturday to determine the sequence of events. Charges are pending.

The wreck forced authorities to close all lanes of westbound I-40 at Airport Boulevard for more than three hours. At one point, a Department of Transportation official said, traffic was backed up as far as Johnston County.

The highway reopened around 4 p.m., but traffic remained heavily congested throughout Friday evening in both the eastbound and westbound lanes, prompting the DOT to issue detours and alternate routes for travelers.